Transmission apparatus, transmission control method, reception apparatus, and reception control method

ABSTRACT

Radio resources are saved. The base station  101  determines a possibility of transmitting data to the terminal  102,  and transmits the indicator indicating the possibility of transmitting the data to the terminal  102.  The terminal  102  generates a mode request message for determining a coding rate and a modulation system at the base station  101,  and sets a transmission frequency of the mode request message based on the indicator transmitted from the base station  101.  Accordingly, the mode request message is transmitted from the terminal  102  to the base station  101  at the determined transmission frequency.

TECHNICAL FIELD

[0001] The present invention relates to a transmission apparatus and amethod for controlling transmission, and further relates to a receivingapparatus and a method for controlling reception. More particularly, thepresent invention relates to, for example in a portable telephonesystem, a transmission apparatus and a method for controllingtransmission capable of saving radio resources and enabling low powerconsumption of a portable telephone, and further relates to a receivingapparatus and a method for controlling reception.

BACKGROUND ART

[0002] An adaptive modulation and coding rate communication system hasbeen proposed to present a high rate communication while sacrificingnoise resistant characteristic to a user who holds a propagation path ofa high quality, and to present a low rate communication while keepingthe noise resistant characteristic to a user who only has a propagationpath of a low quality, by changing the coding rate of an errorcorrection code and the degree of multilevel modulation in accordancewith the quality of the propagation path.

[0003] The adaptive modulation and coding rate communication system ofthis kind (here-in-after referred to as an adaptive and modulationsystem, accordingly) has recently been introduced in a radiocommunication system, and as for one example, there are GSM (GlobalSystem for Mobile Communications), EDGE, HDR (High Data Rate), 1xTREAM,and the like. Further, it is expected that the same communication systemwill be introduced into a communication situation using a W-CDMA(Wideband-Code Division Multiple Access).

[0004] In the situation using the adaptive coding and modulation system,the following fundamental procedures are carried out so as to attain theadaptive coding and modulation on the communication between a basestation and a terminal.

[0005] 1. The terminal determines the received quality of a signal whichis transmitted from the base station.

[0006] 2. The terminal notifies information representing the mostsuitable modulation system and coding rate (here-in-after referred to asa mode request message, accordingly) base on the determination result ofthe received signal quality to the base station.

[0007] 3. The base station determines a modulation system and a codingrate to be actually assigned to the terminal based on a received signalquality message transmitted from the terminal and status of resourcesowned by the base station, and then transmits information representingthe determined modulation system and the coding rate (here-in-afterreferred to as a transmission mode, accordingly) to the terminal.

[0008] 4. The base station encodes and modulates the user data based onthe coding rate and the modulation system corresponding to thetransmission mode, and then transmits to the terminal.

[0009] 5. The terminal receives the transmission mode and carries out adata receiving processing based on the received transmission mode.

[0010] 6. If the terminal detects any error in the received data aftercarrying out the error correction, the terminal transmits aretransmission request, while if the terminal can accurately receive thedata, the terminal transmits a new data transmission request back to thebase station.

[0011] 7. The above steps 1 to 6 are periodically repeated.

[0012]FIG. 1 illustrates a manner of the above mentioned processingsequence. As shown in this figure, illustrated are relations among adownlink control channel for notifying the transmission mode from thebase station to the terminal, a downlink data channel for transmittingthe user data from the base station, and an uplink control channel fortransmitting a transmission mode request message from the terminal. Anexample shown in this figure is the one in which the above-mentionedsteps 1 to 6 are repeated at a predetermined frame period.

[0013] That is, as shown in FIG. 1, the terminal determines the receivedsignal quality at the terminal at the current timing point, and thendetermines a transmission mode to request to the base station based onthe received signal quality. Further, the terminal transmits a moderequest message indicative of the transmission mode to the base stationthrough the uplink control channel.

[0014] The base station determines a transmission mode based on thetransmitted mode request message and radio resources owned by the basestation, then transmits the thus determined transmission mode to theterminal through the downlink control channel. Furthermore, the basestation carries out coding and modulation of the user data based on thecoding rate and the modulation system corresponding to the transmissionmode transmitted to the terminal, and then the transmits to the terminalthrough the downlink data channel.

[0015] Then the terminal receives the transmission mode transmitted fromthe base station in the previous stage, and the terminal recognizes themodulation system and the coding rate of the user data transmitted fromthe base station, thereby. The terminal further receives the user datatransmitted from the base station thereafter and carries out thedemodulation based on the demodulation system which corresponds to themodulation system designated by the transmission mode transmitted inadvance.

[0016] The terminal carries out error detection of the user data whichis obtained by the demodulation and the decoding, and, if no error isdetected, then the terminal transmits a request message for new userdata and a mode request message to the base station through the uplinkcontrol channel, for example.

[0017] On the other hand, if any error is detected in the user dataobtained by carrying out the demodulation and the decoding, then theterminal transmits a retransmission request message requesting that thebase station should retransmit the same user data through the uplinkcontrol channel to the base station. When the base station receives theretransmission request message, then the base station retransmits theuser data again to the terminal.

[0018] The terminal receives the user data retransmitted from the basestation, and carries out the error detection. And if the terminaldetects any error in the user data, then the terminal transmits aretransmission request message again to the base station, and in thisway, the similar processing is repeated. On the other hand, if theterminal detects no error in the user data after carrying out the errorcorrection processing, as described above, the terminal transmits arequest message for new user data and the mode request message to thebase station through the uplink control channel, for example.

[0019]FIG. 1 contains terms of downlink data channel, downlink controlchannel, and uplink control channel. The words “downlink” and “uplink”mean a channel of a signal transmitted from the base station to theterminal and a channel of a signal transmitted from the terminal to thebase station, respectively. That is, the word “downlink” is utilized fora name of a channel through which the signal is transmitted from thebase station to the terminal and the word “uplink” is utilized for aname of a channel through which a signal is transmitted from theterminal to the base station.

[0020] Further, a retransmission request message can employ a flag ofone bit, for example, and in this case, it is able to represent arequest for retransmission if its value is “1”, and to represent arequest for a new user data if it is “0”.

[0021]FIG. 2 is a diagram showing an example of an arrangement of aconventional base station which realizes a communication systememploying an adaptive modulation and coding rate (adaptive coding andmodulation system).

[0022] The base station is arranged to include a transmission/receptioncompatible unit 1, an inverse spreading unit 2, a power control bitextracting unit 3, a retransmission request message extracting unit 4, amode request message extracting unit 5, a mode determining unit 6, acontrol unit 7, a control data generating unit 8, a coding andmodulation unit 9, a power adjusting unit 10, a spreading unit 11, aretransmission buffer 12, an adaptive coding and modulation unit 13, andan antenna 14.

[0023] The base station demodulates the transmitted signal from a userby the transmission/reception compatible unit 1 and the inversespreading unit 2.

[0024] That is, for example, a signal carried out a spectrum spreadingis transmitted to the base station from a terminal capable of doingradio communication composed of a portable telephone, PDA (PersonalDigital Assistant) or the like. The transmitted signal is received bythe antenna 14 and supplied to the transmission/reception compatibleunit 1. The transmission/reception compatible unit 1 is supplied withthe transmission signal from the antenna 14 and subjects the signal to anecessary processing, and then supplies to the inverse spreading unit 2.The inverse spreading unit 2 carries out an inverse spectrum spreadingon the signal supplied from the transmission/reception compatible unit 1and supplies the resultant signal to the power control bit extractingunit 3.

[0025] The power control bit extracting unit 3 extracts a power controlbit from the signal supplied from the inverse spreading unit 2. That is,the transmitted signal to be transmitted from the terminal to the basestation contains the power control bit as a one-bit flag indicating arequest of increase or decrease of power transmitted through thedownlink control channel as described with reference to FIG. 1. Thepower control bit extracting unit 3 extracts this power control bit fromthe signal supplied from the inverse spreading unit 2 and transfers thepower control bit to the power adjusting unit 10.

[0026] The power control bit extracting unit 3 extracts the powercontrol bit from the signal supplied from the inverse spreading unit 2and further supplies the signal to the retransmission request messageextracting unit 4. The retransmission request message extracting unit 4extracts the retransmission request message from the signal suppliedfrom the power control bit extracting unit 3.

[0027] That is, the transmitted signal transmitted from the terminal tothe base station contains the retransmission request message indicatingwhether the user data retransmission is requested or not, as describedwith reference to FIG. 1. The retransmission request message extractingunit 4 extracts the retransmission request message from the signalsupplied from the power control bit extracting unit 3 and transmits theretransmission request message to the control unit 7.

[0028] The retransmission request message extracting unit 4 extracts theretransmission request message from the signal supplied from the powercontrol bit extracting unit 3 and also transmits the signal to the moderequest message extracting unit 5. The mode request message extractingunit 5 extracts the mode request message from the signal supplied fromthe retransmission request message extracting unit 4.

[0029] That is, the transmitted signal transmitted from the terminal tothe base station contains the mode request message indicating thetransmission mode determined based on the received signal quality at theterminal, as described with reference to FIG. 1. The mode requestmessage extracting unit 5 extracts the mode request message from thesignal supplied from the retransmission request message extracting unit4 and then transfers the same to the mode determining unit 6.

[0030] In this case, the signal exchanged between the terminal and thebase station is composed of frames each having a predetermined timespan. Further, each frame is composed of a plural number, e.g., N, ofslots of which time span unit is 0.6667 msec (millisecond), for example.The above described power control bit is arranged so that the powercontrol bit is transmitted from the terminal to the base station at eachslot. Therefore, the power control bit extracting unit 3 extracts thepower control bit at every slot. Further, when the terminal transmitsthe signal, the retransmission request message and the mode requestmessage are disposed at every frame. Therefore, the retransmissionrequest message extracting unit 4 and the mode request messageextracting unit 5 carry out respective extracting operations at everyframe to extract the retransmission request message and the mode requestmessage.

[0031] The mode determining unit 6 determines an optimum modulationsystem and coding rate in accordance with the mode request message andthe state of the resources owned by the base station, and assigns coderesources and power resources to the user (terminal).

[0032] Namely, if there is enough margin in the resources of the basestation, the mode determining unit 6 determines the transmission moderepresented by the mode request message as the transmission mode to beassigned as it is (here-in-after referred to as a assigned transmissionmode, accordingly). On the contrary, if there is not any margin in theresources of the base station, the mode determining unit 6 determinesthe transmission mode which uses less resources as the assignedtransmission mode instead of the transmission mode represented by themode request message.

[0033] Then, when the mode determining unit 6 determines the assignedtransmission mode, then transmits the assigned transmission mode to thecontrol unit 7.

[0034] Initially, the control unit 7 confirms the retransmission requestmessage transmitted from the retransmission request message extractingunit 4, and if it is confirmed that there is a retransmission requestmessage, the control unit 7 transmits information indicative of atransmission mode identical to that upon initially transmitting the userdata (i.e., the transmission mode upon transmitting the user data whichis requested a retransmission) and a retransmission flag indicating thatthis transmission is a retransmission, to the control data generatingunit 8 and the retransmission buffer 12. Further, if there is noretransmission request, the control unit 7 transfers a transmission mode(assigned transmission mode) determined by the mode determining unit 6to the control data generating unit 8 and the adaptive coding andmodulation unit 13.

[0035] The control data generating unit 8 generates control dataincluding the transmission mode to be supplied from the control unit 7,and supplies to the coding and modulation unit 9. If the control datagenerating unit 8 is supplied with a retransmission request flag inaddition to the information indicative of the transmission mode from thecontrol unit 7, the control data generating unit 8 makes theretransmission request flag be involved in the control data. The codingand modulation unit 9 subjects the control data supplied from thecontrol data generating unit 8 to a coding and modulation processingwhich is effected in a predetermined system, then, supplies theresultant modulated signal to the power adjusting unit 10.

[0036] The power adjusting unit 10 determines a level of transmissionpower for transmitting data through the downlink control channeldescribed with reference to FIG. 1, in accordance with the power controlbit supplied from the power control bit extracting unit 3. That is, asdescribed above, the power control bit is a one-bit flag, for example.When the power control bit is “1”, then the power adjusting unit 10increases the transmission power for the downlink control channel by 1dB. When the power control bit is “0”, then the power adjusting unit 10decreases the transmission power for the downlink control channel by 1dB. Thus, the modulated signal supplied from the coding and modulationunit 9 is processed. In this way, it becomes possible to provide anarrangement for transmitting data through the downlink control channelto the terminal at an optimum power. Incidentally, in a communicationusing the CDMA, this manner of controlling the transmission power in thedownlink control channel has been generally employed.

[0037] The modulated signal carried out the transmission poweradjustment in the power adjusting unit 10 is supplied to the spreadingunit 11.

[0038] Meanwhile, the packet data is supplied to the adaptive coding andmodulation unit 13, wherein the user data is allocated in the packetdata and the user data is to be transmitted through the downlink datachannel which is described with reference to FIG. 1. The adaptive codingand modulation unit 13 subjects the packet data to a coding processingby using the coding rate which is indicated in the transmission modeinformation supplied from the control unit 7. Further, the adaptivecoding and modulation unit 13 effects the modulation processing on thecoded packed data by using the modulation system which is indicated inthe transmission mode information. Thus, the modulated signal obtainedby the coding and modulating the packet data is supplied to theretransmission buffer 12.

[0039] In this case, there are provided R=½ and R=¾ as coding rate(coding system) and QPSK (Quadrature Phase Shift Keying) and 16QAM(Quadrature Amplitude Modulation) as modulation system, three kinds oftransmission modes #0 to #2 are explained here. In this case, thetransmission mode is not limited to these three, and is able to preparemany types of modes by the combination of the coding rate and themodulation system.

[0040] The coding rate of R=½ means that a redundant bit of one bit isadded to every one bit of input data. The coding rate of R=¾ means thata redundant bit of one bit is added to every three bits of input data.If the data is coded at the coding rate of R=½, as compared with a casein which the data is coded at the coding rate of R=¾, the whole datacontains a larger number of redundant bits relative to the input data.Therefore, the error correction capability is strengthen but only smallamount of data can be transmitted. Conversely, if the data is coded atthe coding rate of R=¾, as compared with a case in which the data iscoded at the coding rate of R=½, the whole data contains a smallernumber of redundant bits relative to the input data. Therefore, theerror correction capability is inferior to the case in which the data iscoded at the coding rate of R=½ but a large amount of data can betransmitted.

[0041] Further, in the QPSK modulation system, as shown in FIG. 3A, thecoded data are converted into symbols composed of two bits, and thesesymbols are mapped on any of four-symbol group, and in the 16QAMmodulation system, as shown in FIG. 3B, the coded data are convertedinto symbols composed of four bits, and these symbols are mapped on anyof 16-symbol group. If it is assumed that a symbol rate capable of beingtransmitted is constant, the modulation system of the 16QAM has a largeramount of data actually being transmitted than the modulation system ofthe QPSK. However, since the modulation system of the 16QAM has asmaller intersymbol distance than the modulation system of the QPSK, thenoise characteristic is to be deteriorated.

[0042] Now that a combination of the coding rate of R=½ and themodulation system of the QPSK, a combination of the coding rate of R=½and the modulation system of the 16QAM, and a combination of the codingrate of R=¾ and the modulation system of the 16QAM are defined astransmission modes of #0, #1, and #2, respectively, then the relation ofthe data transfer rate among these transmission modes is to be given asfollows. That is, the transmission mode of #0 (R=½, QPSK)<thetransmission mode of #1 (R=½, 16QAM)<the transmission mode of #2 (R=¾,16QAM). On the other hand, the relation of the noise withstandcharacteristic among these transmission modes can be given as follows.That is, the transmission mode of #0 (R=½, QPSK)>the transmission modeof #1 (R=½, 16QAM)>the transmission mode of #2 (R=¾, 16QAM).

[0043] According to the adaptive coding and modulation system, thecoding rate and the modulation system can be selectively determineddepending on the nature of the signal transmission path. That is, if thenoise level is low and the transmission path is good (i.e., the receivedsignal quality at the terminal is good), a combination (transmissionmode) of the coding rate and the modulation system providing a largeamount of data transfer rate is selected to carry out effective datatransmission. Conversely, if the noise level is high and thetransmission path is bad (i.e., the received signal quality at theterminal is bad), a combination of the coding rate and the modulationsystem providing a high noise withstand characteristic (transmissionmode) is selected to carry out data transmission in which the datatransfer rate is suppressed and error correction characteristic isstrengthened.

[0044]FIG. 4 is a diagram showing an arrangement of the adaptive codingand modulation unit 13 in which three transmission modes, i.e., modes of#0 to #2 shown in FIG. 2 are prepared.

[0045] The packet data inputted into the adaptive coding and modulationunit 13 is supplied to a switch 21.

[0046] If the transmission mode information supplied from the controlunit 7 indicates the transmission mode #0, the switch 21 selects aterminal 21 a and a switch 24 selects a terminal 24 a.

[0047] The terminal 21 a is connected to a coding unit 22 a. Therefore,if the transmission mode is of #0, the packet data is supplied from theswitch 21 to the coding unit 22 a. The coding unit 22 a encodes thepacket data supplied thereto at the coding rate of R=½ so that an errorcorrection code is added to the data. The resultant coded data issupplied to a QPSK modulating unit 23 a. The QPSK modulating unit 23 aeffects a QPSK modulation on the coded data supplied from the codingunit 22 a so that modulated symbols are mapped to form a constellation.The resultant modulated signal is supplied to the terminal 24 a of theswitch 24. When the transmission mode is of #0, as described above, theswitch 24 selects the terminal 24 a. Therefore, the modulated signaloutputted from the QPSK modulating unit 23 a is supplied through theswitch 24 to the retransmission buffer 12 (FIG. 2).

[0048] On the contrary, if the transmission mode information suppliedfrom the control unit 7 indicates the transmission mode #1, the switch21 selects a terminal 21 b and the switch 24 selects a terminal 24 b.The terminal 21 b is connected to a coding unit 22 b. Therefore, if thetransmission mode is of #1, the packet data is supplied from the switch21 to the coding unit 22 b. The coding unit 22 b encodes the packet datasupplied thereto at the coding rate of R=½ and the resultant coded datais supplied to a 16QAM modulating unit 23 b. The 16QAM modulating unit23 b effects a 16QAM modulation on the coded data supplied from thecoding unit 22 b and the resultant modulated signal is supplied to theterminal 24 b of the switch 24. When the transmission mode is of #1, asdescribed above, the switch 24 selects the terminal 24 b. Therefore, themodulated signal outputted from the 16QAM modulating unit 23 b issupplied through the switch 24 to the retransmission buffer 12 (FIG. 2).

[0049] Further, if the transmission mode information supplied from thecontrol unit 7 indicates the transmission mode #2, the switch 21 selectsa terminal 21 c and the switch 24 selects a terminal 24 c. The terminal21 c is connected to a coding unit 22 c. Therefore, if the transmissionmode is of #2, the packet data is supplied from the switch 21 to thecoding unit 22 c. The coding unit 22 c encodes the packet data suppliedthereto at the coding rate of R=¾ and the resultant coded data issupplied to a 16QAM modulating unit 23 c. The 16QAM modulating unit 23 ceffects a 16QAM modulation on the coded data supplied from the codingunit 22 c and the resultant modulated signal is supplied to the terminal24 c of the switch 24. When the transmission mode is of #2, as describedabove, the switch 24 selects the terminal 24 c. Therefore, the modulatedsignal outputted from the 16QAM modulating unit 23 c is supplied throughthe switch 24 to the retransmission buffer 12 (FIG. 2).

[0050] Now back to FIG. 2, the retransmission buffer 12 temporary storesthe encoded and modulated user data supplied from the adaptive codingand modulation unit 13, and also supplies to the spreading unit 11.Further when the retransmission buffer 12 receives the retransmissionflag from the control unit 7, then supplies the stored user data againto the spreading unit 11 as the retransmission data. In addition, whenthe retransmission buffer 12 does not receive the retransmission flagfrom the control unit 7, namely when the user data is normally receivedby the terminal, the retransmission buffer 12 erases (deletes) thenormally received data in the stored user data.

[0051] The spreading unit 11 effects the spectrum spreading on themodulated signal supplied from the power adjusting unit 10 and themodulated signal supplied from the retransmission buffer 12 by usingdifferent spreading codes, and supplies thus obtained spread signal tothe transmission/reception compatible unit 1. The transmission/receptioncompatible unit 1 effects a necessary processing on the spread signalsupplied from the spreading unit 11 and transmits to the terminal as aradio wave from the antenna 14.

[0052] In this case, the modulated signal supplied from the poweradjusting unit 10 is to be a signal transmitted through the downlinkcontrol channel shown in FIG. 1 and the modulated signal supplied fromthe adaptive coding and modulation unit 13 is to be a signal transmittedthrough the downlink data channel shown in FIG. 1.

[0053] Next, FIG. 5 is a diagram showing an example of an arrangement ofa conventional terminal which can realize a communication systememploying an adaptive modulation and coding rate (adaptive coding andmodulation system).

[0054] The terminal (user terminal) is arranged to include atransmission/reception compatible unit 31, an inverse spreading unit 32,a control channel received signal quality estimating unit 33, a powercontrol bit generating unit 34, a data channel received signal qualityestimating unit 35, a mode selection unit 36, a control datademodulating and decoding unit 37, a control unit 38, a user datademodulating and decoding unit 39, an error detecting unit 40, aretransmission request message generating unit 41, a retransmissionrequest message inserting unit 42, a mode request message inserting unit43, a power control bit inserting unit 44, a spreading unit 45, and anantenna 46.

[0055] A transmitted signal transmitted from the base station isreceived by the antenna 46. The received signal is subjected to thenecessary processing in the transmission/reception compatible unit 31,and thereafter supplied to the inverse spreading unit 32. The inversespreading unit 32 effects an inverse spectrum spreading on the signalsupplied from the transmission/reception compatible unit 31 so that thesignal is divided into a signal for the downlink data channel and asignal for the downlink control channel which are described withreference to FIG. 1. The inverse spreading unit 32 supplies the signalfor the downlink control channel to the control channel received signalquality estimating unit 33 and the control data demodulating anddecoding unit 37. Further, the inverse spreading unit 32 supplies thesignal for the downlink data channel to the data channel received signalquality estimating unit 35 and the user data demodulating and decodingunit 39.

[0056] The control channel received signal quality estimating unit 33estimates a signal to noise ratio (SNR (Signal to Noise Ratio)) based ona pilot signal which derives from time division multiplexing effected inthe downlink control channel. That is, although description is notprovided with reference to FIG. 2, the spreading unit 11 carries out atime division multiplexing on a predetermined pilot signal with thedemodulated signal supplied from the power adjusting unit 10.Thereafter, the spreading unit 11 carries out the spectrum spreading onthe signal. Therefore, the signal transmitted through the downlinkcontrol channel contains the pilot signal in addition to the modulatedsignal supplied from the power adjusting unit 10. The control channelreceived signal quality estimating unit 33 estimates the SNR of thesignal supplied from the inverse spreading unit 32 through the downlinkcontrol channel by using the pilot signal contained in the signal. Then,the control channel received signal quality estimating unit supplies theestimated SNR to the power control bit generating unit 34.

[0057] The power control bit generating unit 34 responds to theestimated SNR of the downlink control channel in such a manner that ifthe estimated SNR is better than a desired SNR then a power control bitof a value “0” is outputted to the power control bit inserting unit 44while if the same is worse than the desired value then a power controlbit of a value “1” is outputted to the power control bit inserting unit44. In this case, the SNR estimation in the control channel receivedsignal estimating unit 33 and the power control bit generation in thepower control bit generating unit 34 are executed for every slot. Then,the base station described with reference to FIG. 2 controls thetransmission power of the downlink control channel based on the powercontrol bit so that the terminal can always receive the signal of thedownlink control channel at a constant SNR.

[0058] The control data demodulating and decoding unit 37 demodulatesand decodes the signal supplied from the inverse spreading unit 32through the downlink control channel, separates the control data fromthe signal, and supplies the same to the control unit 38.

[0059] The control unit 38 detects the information concerning the codingrate and the modulation system to be applied to the downlink datachannel, i.e., the transmission mode information, which is disposed inthe control data supplied from the control data demodulating anddecoding unit 37. Then, the control unit carries out mode setting(control) for the user data demodulating and decoding unit 39.

[0060] That is, as shown in a flowchart of FIG. 6, initially at step S1,the control unit 38 detects the transmission mode from the control datasupplied from the control data demodulating and decoding unit 37 and theprocessing proceeds to step S2. At step S2, the control unit 38 examineswhether the modulation system indicated by the transmission mode is theQPSK modulation or not. At step S2, if it is determined that themodulation system indicated by the transmission mode is the QPSKmodulation, the processing proceeds to step S3. In this step S3, thecontrol unit 38 demodulates the signal of the downlink data channelbased on the QPSK manner, and controls the user data demodulating anddecoding unit 39 so that this unit decodes the signal at the coding rateof R=½. Thereafter, the control unit 38 awaits the next control data tobe supplied from the control data demodulating and decoding unit 37, andthen, the processing returns from step S3 to S1, and the same processingsequence is repeated in a similar manner.

[0061] At step S2, if it is determined that the modulation systemindicated by the transmission mode is not the QPSK modulation, theprocessing proceeds to step S4. In this step S4, the control unit 38examines whether the modulation system indicated by the transmissionmode is the 16QAM and the coding rate indicated by the transmission modeis R=½ or not. At step S4, if it is determined that the modulationsystem indicated by the transmission mode is the 16QAM and the codingrate indicated by the transmission mode is R=½, then the processingproceeds to step S5. In this step S5, the control unit 38 demodulatesthe signal of the downlink data channel based on the 16QAM manner, andcontrols the user data demodulating and decoding unit 39 so that thisunit decodes the signal at the coding rate of R=½. Thereafter, thecontrol unit 38 awaits the next control data to be supplied from thecontrol data demodulating and decoding unit 37. The processing returnsfrom step S5 to S1, and the same processing sequence is repeated in asimilar manner.

[0062] At step S4, if it is determined that the transmission modeinformation does not designate the combination of the modulation systemof the 16QAM and the coding rate of R=½, the processing proceeds to stepS6. In this step S6, the control unit 38 examines whether the modulationsystem indicated by the transmission mode is the 16QAM or not andwhether the coding rate indicated by the transmission mode is R=¾ ornot. At step S6, if it is determined that the modulation systemindicated by the transmission mode is the 16QAM and the coding rateindicated by the transmission mode is R=¾, then the processing proceedsto step S7. In this step, the control unit 38 demodulates the signal ofthe downlink data channel based on the 16QAM manner, and controls theuser data demodulating and decoding unit 39 so that this unit decodesthe signal at the coding rate of R=¾. Thereafter, the control unit 38awaits the next control data to be supplied from the control datademodulating and decoding unit 37, and then, the processing returns fromstep S7 to S1, and the same processing sequence is repeated in a similarmanner.

[0063] At step S6, if it is determined that the transmission modeinformation does not designate the combination of the modulation systemof the 16QAM and the coding rate of R=¾, this determination means thatthe transmission mode information does not designate the above mentionedthree combinations of the modulation system and the coding rate. In thisevent, the control unit 38 determines that the transmission mode iserroneous one, and hence the control unit takes no particular action incontrolling the user data demodulating and decoding unit 39. Thus, thecontrol unit 38 awaits the next control data to be supplied from thecontrol data demodulating and decoding unit 37, and the processingreturns from step S6 to S1, and the same processing sequence is repeatedin a similar manner.

[0064] Now description will be again made with reference to FIG. 5. Thedata channel received signal quality estimating unit 35 estimates theSNR of the signal of the downlink data channel supplied from the inversespreading unit 32. When the data channel received signal qualityestimating unit 35 estimates the SNR, the data channel received signalquality estimating unit 35 utilizes a pilot symbol subjected to the timedivision multiplexing on the downlink data channel or a pilot channelsymbol transmitted together with the downlink data channel in a parallelmanner.

[0065] Although description is not provided yet with reference to FIG.2, the spreading unit 11 effects the time division multiplexing on thepredetermined pilot signal with the demodulated signal supplied from theadaptive coding and modulation unit 13. Thereafter, the spreading unit11 carries out the spectrum spreading. Therefore, the signal of thedownlink data channel contains the pilot signal. Further, the spreadingunit 11 effects the spectrum spreading on another pilot signal with aspreading code different from a spreading code which is utilized for theeffecting spectrum spreading on the demodulated signal supplied from thepower adjusting unit 10 or the adaptive coding and modulation unit 13.Then, the pilot signal is supplied through the transmission/receptioncompatible unit 1 to the antenna 14 from which the pilot signal istransmitted through the downlink data channel and the downlink controlchannel in parallel.

[0066] The data channel received signal quality estimating unit 35estimates the SNR of the signal of the downlink data channel suppliedfrom the inverse spreading unit 32 by using the pilot signal containedin the signal or the pilot signal transmitted in parallel together withthe signal of the downlink data channel. Then, the estimated SNR issupplied to the mode selection unit 36.

[0067] The mode selection unit 36 recognizes the estimated SNR of thedownlink data channel supplied from the data channel received signalquality estimating unit 35 as the received signal quality at theterminal, and determines (selects) the combination, namely thetransmission mode, of the coding rate and modulation system capable ofsetting the error rate of the user data to be equal or less than thepredetermined value relative to the received signal quality. Further,the mode selection unit 36 generates a mode request message indicatingits transmission mode as to request thus determined transmission mode tothe base station, and supplies to the mode request message insertingunit 43.

[0068] In this case, the data channel received signal quality estimatingunit 35 estimates the SNR of the downlink data channel for each frame,and the mode selection unit 36 generates the mode request message alsoat every frame.

[0069] In this case, if it is estimated that the noise level of thetransmission path is small, accordingly, the transmission path is better(when the received signal quality is better) based on the receivedsignal quality supplied from the data channel received signal qualityestimating unit 35, the mode selection unit 36 selects the transmissionmode combining the coding rate and the modulation system which are ableto handle higher transmission rate data. Conversely, if it is estimatedthat the noise level of the transmission path is high and, accordinglythe transmission path is bad (when the received signal quality isextremely bad), the transmission mode combining the coding rate and themodulation system which are able to suppress the rate of the datatransmission and to strengthen the error correction.

[0070] More specifically, the mode selection unit 36, as shown in FIG.7, for example, selects the transmission mode capable of setting theerror rate of the user data to be equal or less than the predeterminedvalue.

[0071] Namely, FIG. 7 shows a relation between the received signalquality and the error rate of the user data (FER: Frame Error Rate) withrespect to above mentioned respective three transmission modes #0 (R=½,QPSK), #1 (R=½, 16QAM), and #2 (R=¾, 16QAM). The mode selection unit 36,for example, selects the transmission mode capable of setting the errorrate (FER) of the user data to be equal or less than 10% relative to thereceived signal quality. In this case, according to FIG. 7, the modeselection unit 36 selects the transmission modes #0 (R=½, QPSK), #1(R=½, 16QAM), or #2 (R=¾, 16QAM), respectively in case when the receivedsignal quality is below −8 db, larger than −8 db and smaller than −4 db,or more than −4 db.

[0072] On the other hand, the user data demodulating and decoding unit39 carries out decoding and demodulation on the signal of the downlinkdata channel supplied from the inverse spreading unit 32 under thecontrol of the control unit 38 which is described with reference to FIG.6. The resultant user data obtained by the operation is supplied to theerror detecting unit 40. When the user data demodulating and decodingunit 39 decodes the signal of the downlink data channel, the user datademodulating and decoding unit 39 carries out user data error correctionby using the error correction code contained in the signal as aredundancy bit.

[0073] The error detecting unit 40 carries out a parity detection byusing Cyclic Redundancy Check (CRC), for example. That is, the errordetecting unit 40 examines whether the user data decoded by the userdata demodulating and decoding unit 39 contains error or not, and theerror detecting unit 40 supplies the result of the examination to theretransmission request message generating unit 41.

[0074] If the retransmission request message generating unit 41 receivesan examination result indicating that there is no error containedtherein from the error detecting unit 40, then the retransmissionrequest message generating unit 41 generates a message having a value of“0”, for example, and supplies the message to the retransmission requestmessage inserting unit 42. Conversely, if the retransmission requestmessage generating unit 41 receives an examination result indicatingthat there is some error contained therein from the error detecting unit40, then the retransmission request message generating unit 41 generatesa message having a value of “1”, for example, and supplies the messageto the retransmission request message inserting unit 42.

[0075] The retransmission request message inserting unit 42 carries outframing on the retransmission request message supplied from theretransmission request message generating unit 41 with the signal of theuplink control channel described with reference to FIG. 1, and suppliesthe resultant signal to the mode request message inserting unit 43. Themode request message inserting unit 43 carries out framing on the moderequest message supplied from the mode selection unit 36 with the signalof the uplink control channel supplied from the retransmission requestmessage inserting unit 42. The resultant signal is supplied to the powercontrol bit inserting unit 44. The power control bit inserting unit 44carries out framing on the power control bit supplied from the powercontrol bit generating unit 34 with the signal of the uplink controlchannel supplied from the mode request message inserting unit 43. Theresultant signal is supplied to the spreading unit 45. The spreadingunit 45 effects the spectrum spreading on the signal of the uplinkcontrol channel transmitted from the power control bit inserting unit44, and supplies the resultant signal obtained by the operation to thetransmission/reception compatible unit 31. The transmission/receptioncompatible unit 31 effects a necessary processing on the spread signaltransmitted from the spreading unit 45 and transmits the signal throughthe antenna 47.

[0076] As described above, according to the adaptive coding andmodulation system, the terminal informs (requests) a desirablecombination (transmission mode) of the modulation system and coding rateto the base station based on the received signal quality, then the basestation is able to select the combination of the modulation system andthe coding system to be actually assigned based on this, so that itbecomes possible to change the data transmission speed based on thereceiving condition (received signal quality) at the terminal, andaccordingly the data can be transmitted to the terminal moreeffectively.

[0077] However, it is impossible for the terminal to determine when theuser data is transmitted, so that it is necessary to always transmit amode request message to the base station. The uplink wireless resourcesare employed when the mode request message is transmitted to the basestation, so that interferences become huge when there are a lot ofterminals. Further, in the base station, the transmission of moderequest massage from the terminal to the base station, although there isno data to be transmitted to the terminal, causes useless powerconsumption in the terminal.

DISCLOSURE OF THE INVENTION

[0078] The present invention is made in view of the above aspect.Therefore, it is an object of the present invention to propose asolution in which unnecessary transmission of the mode request messageand the like is suppressed, and saving of the uplink radio resources isrealized.

[0079] A transmission apparatus of the present invention ischaracterized by including, determination means for determining apossibility of transmitting data to a receiving apparatus, andtransmission means for transmitting a possibility information indicatinga possibility of transmitting the data to the receiving apparatus andfrequency information designating a transmission frequency to thereceiving apparatus.

[0080] A method for controlling transmission of the present invention ischaracterized by including a determination step for determining apossibility of transmitting data to a receiving apparatus, and atransmission control step for transmitting a possibility informationindicating a possibility of transmitting the data to the receivingapparatus and frequency information designating a transmission frequencyto the receiving apparatus.

[0081] A first program of the present invention is characterized byincluding a determination step for determining a possibility oftransmitting data to a receiving apparatus, and a transmission controlstep for transmitting a possibility information indicating a possibilityof transmitting the data to the receiving apparatus and frequencyinformation designating a transmission frequency to the receivingapparatus.

[0082] A receiving apparatus of the present invention is characterizedby including generating means for generating a predetermined informationfor determining a coding rate and a modulation system at a transmittingapparatus, setting means for setting a transmission frequency of apredetermined information based on a possibility information indicatinga possibility of transmitting data from the transmitting apparatus, andtransmitting means for transmitting the predetermined information to thetransmitting apparatus at the transmission frequency set by the settingmeans.

[0083] A method for controlling reception of the present invention ischaracterized by including a generating step for generating apredetermined information for determining a coding rate and a modulationsystem at a transmitting apparatus, a setting step for setting atransmission frequency of a predetermined information based on apossibility information indicating a possibility of transmitting datafrom the transmitting apparatus, and a transmitting step fortransmitting the predetermined information to the transmitting apparatusat the transmission frequency set by the setting means.

[0084] A second program of the present invention is characterized byincluding a generating step for generating a predetermined informationfor determining a coding rate and a modulation system at a transmittingapparatus, a setting step for setting a transmission frequency of apredetermined information based on a possibility information indicatinga possibility of transmitting data from the transmitting apparatus, anda transmitting step for transmitting the predetermined information tothe transmitting apparatus at the transmission frequency set by thesetting means.

[0085] A communication system of the present invention is characterizedby including determining means for determining a possibility oftransmitting data to a receiving apparatus, a first transmitting meansfor transmitting a possibility information indicating a possibility oftransmitting the data to the receiving apparatus to the receivingapparatus, generating means for generating a predetermined informationfor determining a coding rate and a modulation system at a transmittingapparatus, setting means for setting a transmission frequency for thepredetermined information based on the possibility informationtransmitted from the transmitting apparatus, and a second transmittingmeans for transmitting the predetermined information to the transmittingapparatus at the transmission frequency set by the setting means.

[0086] In a transmitting apparatus, a method for controllingtransmission, and a first program, a possibility of transmitting data toa receiving apparatus is determined, and a possibility informationindicating a possibility of transmitting the data to the receivingapparatus and a frequency information designating transmission frequencyfor a predetermined information are transmitted.

[0087] In a receiving apparatus, a method for controlling reception, anda second program, a predetermined information for determining a codingrate and a modulation system at a transmitting apparatus is generated,and a transmission frequency for the predetermined information is set.And, the predetermined information is transmitted to the transmittingapparatus at the set transmission frequency.

[0088] In a communication system of the present invention, a possibilityof transmitting data to a receiving apparatus is determined, and apossibility information indicating a possibility of transmitting data tothe receiving apparatus is transmitted to the receiving apparatus.Further, a predetermined information for determining a coding rate and amodulation system at a transmitting apparatus is generated, and atransmission frequency for the predetermined information is set based onthe possibility information transmitted from the transmitting apparatus.Accordingly, the predetermined information is transmitted to thetransmitting apparatus at the set transmission frequency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0089]FIG. 1 is a diagram for explaining a conventional manner of datatransmission;

[0090]FIG. 2 is a block diagram showing one example of an arrangement ofa conventional base station;

[0091]FIG. 3A is a diagram illustrating the mapping of the data inaccordance with a QPSK modulation system;

[0092]FIG. 3B is a diagram illustrating the mapping of the data inaccordance with a 16QAM modulation system;

[0093]FIG. 4 is a block diagram showing an example of an arrangement ofan adaptive coding and modulation unit 13;

[0094]FIG. 5 is a block diagram showing one example of an arrangement ofa conventional terminal;

[0095]FIG. 6 is a flowchart for explaining a data receiving processingat a control unit;

[0096]FIG. 7 is a chart showing a relation between the received signalquality and the error rate;

[0097]FIG. 8 is a block diagram showing one example of a transmissionsystem to which the present invention is applied;

[0098]FIG. 9 is a block diagram showing one example of the base station101;

[0099]FIG. 10 is a block diagram showing one example of the terminal102;

[0100]FIG. 11 is a flowchart showing a processing at the base station101;

[0101]FIG. 12 is a flowchart showing a processing at the terminal 102;

[0102]FIG. 13 is a flowchart showing a processing at the terminal 102;

[0103]FIG. 14 is a flowchart showing a processing at the terminal 102;

[0104]FIG. 15 is a flowchart showing a processing at the terminal 102;

[0105]FIG. 16 is a chart showing communications between the base station101 and the terminal 102; and

[0106]FIG. 17 is a block diagram showing an example of an arrangement ofone embodiment as a computer to which the present invention is applied.

BEST MODE FOR CARRYING OUT THE INVENTION

[0107]FIG. 8 is a diagram showing an example of an arrangement of oneembodiment of a communication system (the system means a thing formed bygathering a plurality of apparatuses, and it is not concerned whethereach construction of apparatuses are included in a housing or not.) towhich the present invention is applied.

[0108] The communication system in FIG. 8 comprises of a base station101 and a terminal 102 such as a mobile telephone or the like, forexample, and data is to be communicated between the base station 101 andthe terminal 102 by radio communications.

[0109] In this case, in the mode of the embodiment in FIG. 8, only eachone of the base station 101 and the terminal 102 is respectivelydepicted, but the communication system is possible to be constructedwith a plurality of base stations and terminals.

[0110]FIG. 9 shows one constructive example of the base station 101 inFIG. 8. In this case, in this figure, the portions corresponding to themin FIG. 2 are assigned the same references, and here-in-after, theirexplanations are omitted here by case.

[0111] As shown in FIG. 9, the base station is arranged to include atransmission/reception compatible unit 1, an inverse spreading unit 2, apower control bit extracting unit 3, a retransmission request messageextracting unit 4, a mode request message extracting unit 5, a modedetermining unit 6, a control unit 7, a coding and modulation unit 9, apower adjusting unit 10, a spreading unit 11, a retransmission buffer12, an adaptive coding and modulation unit 13, a data buffer 111, and acontrol data generating unit 112.

[0112] Accordingly, the base station shown in FIG. 9 is newly providedwith the data buffer 111, and further the control data generating unit112 is also provided instead of the control data generating unit 8.Other portions are basically constructed as the base station in FIG. 2.

[0113] In this case, in the mode of the embodiment in FIG. 9, the databuffer 111 and the retransmission buffer 112 are depicted one in each,but the data buffer 111 and the retransmission buffer 112 are preparedto each of user who is registered to the base station 101. Namely, thebase station 101 handles, for example, communications among terminalsexisted at an area (cell) within a range of a predetermined distance,but the data buffer 111 and the retransmission buffer 112 are preparedper each terminal that is handled by the corresponding base station 101.

[0114] The data buffer 111 temporally stores packet data to which theuser data is allocated and which is to be inputted to the base station101, and supplies to the adaptive coding and modulation unit 13 when itis necessary.

[0115] The control data generating unit 112 operates to include a dataindicator bit to conventional control data, and transmits.

[0116] Namely, the control data generating unit 112 determinespossibility of transmission of data to the terminal 102, and suppliesthe data indicator bit (here-in-after, simply referred to as anindicator) by including in the control data to the adaptive coding andmodulation unit 9.

[0117] More specifically, the control data generating unit 112 watchesthe data buffer 111 and the retransmission buffer 12, and if the dataaddressed to the terminal 102 is stored in either the data buffer 111 orthe retransmission buffer 12, then generates the indicator indicatingthe possibility of transmission of data to the terminal 102, namely theindicator having a value of “1”, for example, and includes in thecontrol data. Further, if the data addressed to the terminal 102 is notstored in neither the data buffer 111 nor the retransmission buffer 12,then the control data generating unit 112 generates the indicatorindicating the possibility of transmission of data to the terminal 102,namely the value of the indicator having a value of “0”, for example,and includes in the control data.

[0118] Further, in the above identified case, simply if the dataaddressed to the terminal 102 is stored in either the data buffer 111 orthe retransmission buffer 12, then the indicator having a value of “1”is generated as the fact that there is a possibility of transmission ofdata to the terminal 102. But setting the indicator to be “1”, namelythe possibility of the transmission of data to the to the terminal 102is able to be determined by considering whether the user data is notassigned to the terminal 102 within a predetermined time or not (theuser data addressed to the terminal 102 stored in either data buffer 111or the retransmission buffer 12 are not transmitted more thanpredetermined interval), or whether more than predetermined bits of theuser data addressed to the terminal 102 are existed either in the databuffer 111 or the retransmission buffer 12 or not, in addition to theexistence of the data in the data buffer 111 and the retransmissionbuffer 12.

[0119] Further as will be described later, when a transmission cycle Mis not M=∞, but a certain finite value, namely when the mode requestmessage is transmitted from the terminal 102 back to the base station101 at every M frames, it is able to set the indicator to be “1”provided that a mean received signal quality at the terminal 102 exceedsa predetermined threshold value.

[0120] Namely, the case where the indicator is “1” means that here is apossibility of transmission of data to the terminal 102 now.

[0121] On the contrary, the base station 101 assigns radio resources tothe terminal 102 and, in addition, a lot of terminals including otherterminals (not shown), and after that, transmits data addressed to theseterminals. Accordingly, although the user data addressed to the terminal102 are existed either in the data buffer 111 or retransmission buffer12, the user data is not always transmitted immediately to the terminal102.

[0122] Namely, the base station 101 assigns the radio resources to eachterminal based on, for example, the data amount of the user data foreach terminal stored in either the data buffer 111 or the retransmissionbuffer 12, or how long the user data for each terminal stored in eitherthe data buffer 111 or the retransmission buffer 12 is stored withoutany transmission, or further based on the mean received signal qualityor the like at each terminal.

[0123] Specifically, the base station 101 preferentially assigns, forexample, the radio resources to the terminal having more data amount ofthe user data stored in either the data buffer 111 or the retransmissionbuffer 12. Further the base station 101 preferentially assigns the radioresources to the terminal that stores longer the user data stored ineither the data buffer 111 or the retransmission buffer 12 storedwithout any transmission. Further, the base station 101 preferentiallyassigns the radio resources to the terminal that has higher meanreceived signal quality.

[0124] Accordingly, the user data addressed to the terminal 102 ispreferentially transmitted based on not only the fact that the user dataaddressed to the terminal 102 is stored in either the data buffer 111 orthe retransmission buffer 12 but also the fact that its amount of thedata is large, or its user data is not transmitted for a long time, andfurther the fact that the mean received signal quality at the terminal102 is high, so that it is probable that the data is to be transmittedto the terminal 102, now.

[0125] Then, when the user data addressed to the terminal 102 is storedeither in the data buffer 111 or the retransmission buffer 12 andfurther its data amount is large, when its user data is not transmittedfor a long time, or the mean received signal quality is high, it is ableto set the value of the indicator to be “1” indicating that there is apossibility of transmitting the data to the terminal 102.

[0126] In addition, the mean received signal quality at the terminal 102is, for example, able to be obtained from the mode request message to beextracted at the mode request message extracting unit 6. Namely, thetransmission mode indicated by the mode request message is determined atthe terminal 102 based on the received signal quality at the terminal102 similar to the case explained in FIG. 5. Namely, based on thetransmission mode indicated by the mode request message, it is possibleto estimate the received signal quality, and accordingly, it is able toobtain the mean received signal quality at the terminal 102 based onthus estimated received signal quality.

[0127] The control data generating unit 112 determines the possibilityof transmitting the data to the terminal 102 as described above,includes the indicator indicating the possibility into the control data,and further generates frequency information designating transmissionfrequency of the mode request message from the terminal 102, andincludes in the control data.

[0128] Namely, the control data generating unit 112 sets thetransmission frequency so that the transmission cycle becomes at every Kframes, for example, in the case where the indicator is “1”, and thereis a possibility of transmitting data to the terminal 102, and furthersets the transmission frequency so that the transmission cycle becomesat every M frames where M is larger than K, for example, in the casewhere the indicator is 0, and there is no possibility of transmittingdata to the terminal 102. Namely, control data generating unit 112 setsa lower transmission frequency when the indicator is “0” than when theindicator is “1” if the transmission frequency when the indicator is “1”is taken as a reference.

[0129] More specifically, the control data generating unit 112adaptively sets (controls) respective transmission frequency in thecases of indicator to be “0” or “1”, based on the traffic of thetransmission path, namely the number of the terminals registered to thebase station 101.

[0130] In this case, if the frequency information represents, forexample, the transmission cycle transmitted by allocating the moderequest message in the frame, then it is possible to set its value to bea finite value, but it is also possible to set the transmission cycle inthe case where the indicator is “0” to be infinite value. In this case,the terminal 102 does not transmit the mode request message to the basestation 101.

[0131] Further, the transmission cycle in the case where the indicatoris “1” is possibly set to be “1”, for example. The mode request messageis to be transmitted at every one frame from the terminal 102 to thebase station 101.

[0132] In this case, in the above case, it is possible to set thefrequency information K in the case where the indicator is “1”, and thefrequency information M in the case of the indicator is “0” to be anyvalue in the control data generating unit 112. On the contrary, thefrequency information K or M is able to be previously determined to afixed value corresponding to respective indicator having value of “1” or“0”. As described above, when the frequency information K and M ispreviously determined, it is not necessary to include the frequencyinformation K and M in the control data together with the indicator.

[0133] Namely, in the case where the frequency information K or M ispreviously determined corresponding to respective indicator having avalue of “1” or “0”, the transmission frequency of the mode requestmessage is to be uniquely determined by the value of the indicator.Accordingly, in this case, the frequency information K and M are to beequivalently included in the control data by including the indicator,even if the frequency information K and M is not included.

[0134] Next, FIG. 10 shows one constructive example of the terminal 102in FIG. 8. In this case, in this figure, the parts corresponding partsin FIG. 5 are assigned the same references and here-in-after the theseexplanations are omitted, accordingly.

[0135] As shown in FIG. 10, the terminal (user terminal) is arranged toinclude a transmission/reception compatible unit 31, an inversespreading unit 32, a control channel received signal quality estimatingunit 33, a power control bit generating unit 34, a data channel receivedsignal quality estimating unit 35, a mode selection unit 36, a controldata demodulation and decoding unit 37, a control unit 38, a user datademodulation and decoding unit 39, an error detecting unit 40, aretransmission message generating unit 41, a retransmission requestmessage inserting unit 42, a mode request message inserting unit 42, apower control bit inserting unit 44, a spreading unit 45, an antenna 46,and a transmission mode determining unit 121.

[0136] Accordingly, the terminal 102 shown in FIG. 9 is newly providedwith the transmission mode determining unit 121, and other portions arebasically constructed as the terminal in FIG. 5.

[0137] The control data demodulated and decoded at the control datademodulation and decoding unit 37 is supplied to the transmission modedetermining unit 121. The transmission mode determining unit 121controls the operation of the data channel received signal qualityestimating unit 35 based on the indicator and the frequency informationincluded in the control data.

[0138] Namely, suppose that the frequency information indicates that thetransmission frequency is set to be every M or K frames when theindicator is “0” and when the indicator is “0”, then the transmissionmode determining unit 121 controls the data channel received signalquality estimating unit 35 as to estimate the received signal quality ofthe downlink data channel at every M frames when the indicator includedin the control data is “0”, and further, controls the data channelreceived signal quality estimating unit 35 as to estimate the receivedsignal quality of the downlink data channel at every K (<M) frames whenthe indicator included in the control data is “b 1”.

[0139] In this case, when the received signal quality is supplied fromthe data channel received signal quality estimating unit 35, the modeselection unit 36 determines the transmission mode based on its receivedsignal quality, and supplies to the mode request message inserting unit43. Accordingly, when the data channel received signal qualityestimating unit 35 is controlled as to estimate the received signalquality at every M or K frames, the transmission mode is to betransmitted at the terminal 102 at every M or K frames in the terminal102.

[0140] In this case, as above described, when the frequency informationK or M is previously determined with reference to the indicator having avalue of “1” or “0”, the transmission mode determining unit 121determines uniquely the frequency information K or M by the value of theindicator included in the control data, and controls the data channelreceived signal quality estimating unit 35.

[0141] Next, a processing of the base station 101 in FIG. 9 is explainedwith reference to a flowchart in FIG. 11.

[0142] At first, at step S11, the control data generating unit 112determines whether there is a possibility of transmitting either theuser data or the retransmission data for the terminal 102 or not withreference to the data buffer 111 and the retransmission buffer 12, forexample.

[0143] At step S11, if it is determined that there is a possibility oftransmitting the user data or the retransmission data for the terminal102, the processing proceeds to step S12, and a variable ind designatingthe indicator is set to be “1”, and is transmitted together with thefrequency information K indicating the transmission frequency of themode request message in case that the indicator is “1”, then theprocessing proceeds to step S14.

[0144] Namely, at step S12, the control data generating unit 112generates the control data including the indicator ind having the valueof “1” and the frequency information. This control data is supplied fromthe control data generating unit 112 through the coding and modulationunit 9, the power adjusting unit 10, the spreading unit 11, and thetransmission/reception compatible unit 1 to the antenna 14, and istransmitted as the signal of the downlink control channel.

[0145] On the other hand, at step S12, if it is determined that there isno possibility of transmitting the user data or the retransmission datafor the terminal 102, the processing proceeds to step S13, and thevariable ind designating the indicator is set to be “0”, and istransmitted together with the frequency information K indicating thetransmission frequency of the mode request message in case that theindicator ind is “0”, then the processing proceeds to step S14.

[0146] Namely, at step S13, the control data generating unit 112generates the control data including the indicator ind having the valueof ‘0’ and the frequency information M. This control data is suppliedfrom the control data generating unit 112 through the coding andmodulation unit 9, the power adjusting unit 10, the spreading unit 11,and the transmission/reception compatible unit 1 to the antenna 14, andis transmitted as the signal of the downlink control channel.

[0147] At step S14, the signal of the uplink control channel transmittedfrom the terminal 102 is received.

[0148] Namely, the signal of the uplink control channel transmitted fromthe terminal 102 is received at the antenna 14, and supplied trough thetransmission/reception compatible unit 1 and inverse spreading unit 2 tothe power control bit extracting unit 3.

[0149] Then, the processing proceeds to step S15, the power control bitextracting unit 3 extracts a power control bit from the signal of theuplink control channel supplied thereto, supplies the power control bitto the power adjusting unit 10, and further supplies the signal of theuplink control channel to the retransmission request message extractingunit 4, then the processing proceeds to step S16.

[0150] At step S16, the power adjusting unit 10 adjusts the transmissionpower of the downlink control channel in response to the power controlbit from the power control bit extracting unit 3, and the processingproceeds to step S17. At step S17, the retransmission request messageextracting unit 4 extracts the retransmission request message from thesignal from the uplink control channel supplied thereto, supplies theretransmission request message to the control unit 7, and furthersupplies the signal of the uplink control channel to the mode requestmessage extracting unit 5.

[0151] Then, the processing proceeds to step S18, and the control unit 7determines whether the terminal 102 is able to normally receive the userdata based on the retransmission request message supplied from theretransmission request message extracting unit 4. At step S18, if it isdetermined that the terminal 102 is able to normally receive the userdata, namely, the retransmission request message is not a request forretransmission, but a request for transmitting new data, the processingproceeds to step S19, and the control unit 7 erases the user datanormally received at the terminal 102 among the retransmission datastored therein by controlling the retransmission buffer 12, then theprocessing proceeds to step S20.

[0152] In case when, at step S18, it is determined that terminal 102 isnot able to normally receive the user data, namely, the retransmissionrequest message is a request for retransmission, the control unit 7recognizes the user data which is requested the retransmission, then theprocessing proceeds to step S20 while skipping the step S19.Accordingly, in this case, the retransmission buffer 12 remains in acondition where the retransmission data corresponding to the user datathat is requested the retransmission are stored.

[0153] At step S20, the mode request message extracting unit 5 extractsthe mode request message form the signal of the uplink control channelsupplied from the retransmission request message extracting unit 4, andsupplies to the mode determining unit 6, then the processing proceeds tostep S21.

[0154] At step S21, the mode determining unit 6 determines the codingrate and the modulation system (transmission mode) at the adaptivecoding and modulation unit 13 based on the transmission mode requestedfrom the terminal 102 and represented by the mode request messagesupplied from the mode request message extracting unit 5 and the radioresources owned by the base station 101. Further, at step S16, the modedetermining unit 6 supplies the determined transmission mode to thecontrol unit 7, then the processing proceeds to step S22.

[0155] At step S22, the control unit 7 determines whether the user dataaddressed to the terminal 102 is stored in the data buffer 111 or not.At step S22, if it is determined that the user data addressed to theterminal 102 is stored in the data buffer 111, then the processingproceeds to step S23, and the control unit 7 supplies the transmissionmode supplied from the mode determining unit 6 at previous step to thecontrol data generating unit 8, and the control data generating unit 8generates the control data including its transmission mode. This controldata is supplied from the control data generating unit 8 through thecoding and modulation unit 9, the power adjusting unit 10, the spreadingunit 11, and the transmission/reception compatible unit 1 to the antenna14, and is transmitted as the signal of the downlink control channel.

[0156] After that, the processing proceeds to step S24, the user datafor the terminal 102 stored in the data buffer 111 is transmitted withthe transmission mode determined by the mode determining unit 6, andalso the user data is stored in the retransmission buffer 12 as theretransmission data.

[0157] Namely, at step S24, the packet data, in which the user data forthe terminal 102 stored in the data buffer 111 are allocated, istransferred from the data buffer 111 to the adaptive coding andmodulation unit 13. Then the control unit 7 controls the adaptive codingand modulation unit 13 as to carry out the encoding and modulation ofthe user data (the packet data in which the user data is allocated) forthe terminal 102 with the transmission mode determined at the modedetermining unit 6. The adaptive coding and modulation unit 13 encodesand modulates the user data for the terminal 102 supplied from the databuffer 111 in accordance with the control by the control unit 7, andsupplies through the retransmission buffer 12 to the spreading unit 11,and further supplies to the retransmission buffer 12 to store as theretransmission data. Here-in-after, in the spreading unit 11 and thetransmission/reception compatible unit 1, the same processing is carriedout as explained in FIG. 2, and thereby the user data is transmittedfrom the antenna 14 to the terminal 102 as the signal of the downlinkdata channel.

[0158] As described above, the processing proceeds back to step S11after the user data is transmitted, and the similar processing isrepeated here-in-after.

[0159] On the contrary, at step S22, if it is determined that the userdata addressed to the terminal 102 is not stored in the data buffer 111,then the processing proceeds to steps S25 to S27, and the transmission(retransmission) of the retransmission data stored in the retransmissionbuffer 12 is carried out.

[0160] Namely, at step S25, the control unit 7 determines whether thereis a request for retransmission of the user data corresponding to theretransmission data or not, and whether the retransmission data for theterminal 102 stored in the retransmission buffer 12 or not.

[0161] At step S25, if it is determined that the retransmission data forthe terminal 102 is not stored in the retransmission buffer 12, or thateven it is stored, there is not any request for retransmission of theretransmission data, the processing proceeds back to step S11 byskipping steps S26 and S27, and then the similar processing is repeatedhere-in-after.

[0162] Further, at step S25, if it is determined that the retransmissiondata for the terminal 102 is stored in the retransmission buffer 12 andthere is a request for retransmission of the user data corresponding tothe retransmission data, the processing proceeds to step S26, and thecontrol unit 7 supplies the transmission mode, which is the sametransmission mode used when the user data corresponding to theretransmission data, to the control data generating unit 8, and thecontrol data generating unit 8 generates the control data including itstransmission mode. This control data is supplied from the control datagenerating unit 8 through the coding and modulation unit 9, the poweradjusting unit 10, the spreading unit 11, and the transmission/receptioncompatible unit 1 to the antenna 14, and is transmitted as the signal ofthe downlink control channel.

[0163] After that, the processing proceeds to step S27, theretransmission data requested the retransmission and stored inretransmission buffer 12 is read out, and supplied to the spreading unit11. Here-in-after, in the spreading unit 11 and thetransmission/reception compatible unit 1, the same processing is carriedout as explained in FIG. 2, and thereby the retransmission data istransmitted (retransmitted) from the antenna 14 to the terminal 102 asthe signal of the downlink data channel.

[0164] As described above, the processing proceeds back to step S11after the retransmission data is transmitted (retransmitted), and thesimilar processing is repeated here-in-after.

[0165] As described above, the base station 101 determines thepossibility of transmitting the data to the terminal 102, and transmitsthe indicator ind indicative of the determined result to the terminal102, so that the terminal 102 is possible to change the transmissionfrequency of the mode request message to the base station 101.

[0166] Further the base station 101 is possible to transmit thefrequency information representing the transmission frequency for themode request message, and in this case, it is possible to adaptivelycontrol the transmission frequency of the mode request message to thebase station 101 by the terminal 102 in response to status of load inthe base station 101.

[0167] Next, the processing by the terminal 102 in FIG. 2 is explained.

[0168] At the terminal 102, the signal of the downlink control channelis decoded and demodulated, and the indicator ind is obtained.Successively, it is determined whether the indicator is “0” or “1”, andif “0”, it is carried out the control where the mode request message tofeed back the received signal quality of the terminal 102 to the basestation is transmitted to the base station 101 at every M frames.

[0169] On the contrary, if the indicator bit is “1”, it is carried outthe control where the mode request message is transmitted to the basestation 101 at every K frames, where K is smaller than M. Further, theterminal 102 checks the transmission mode among the control dataincluded in the downlink control channel, and determines that thereceived data is transmitted by encoding which coding rate, andmodulated by which modulation system. Namely, in the mode of the presentembodiment, it is determined that the transmission mode is one of threetransmission modes #0 to #2 comprised of a combination of QPSK and R=½,16QAM and R=½, and 16QAM and R=¾, respectively. Then, the appropriatedemodulation and the decoding are carried to the received data inresponse to its transmission mode, and here-in-after, the similarprocessing is repeated.

[0170] Next, the processing of the terminal 102 in FIG. 10 is furtherexplained with reference to flowcharts in FIGS. 12 to 15.

[0171] Now, with reference to the flowchart in FIG. 12, the processingrelating to the downlink control channel and the downlink data channelfor processing the signals of the downlink control channel and thedownlink data channel carried out by the terminal 102 is explained.

[0172] At first, at step S31, the signals from the downlink controlchannel and the downlink control channel transmitted from the basestation 101 are received. Namely, at step S31, the signals from thedownlink control channel and the downlink data channel transmitted fromthe base station 101 are received by the antenna 46, and supplied to theinverse spreading unit 32 after carried out necessary processing at thetransmission/reception compatible unit 31. Further, at step S31, theinverse spreading unit 32 separates the signal from thetransmission/reception compatible unit 31 by carrying out the spectruminverse spreading processing into the signal of the downlink datachannel and the signal of the downlink control channel shown in FIG. 1.Then, the inverse spreading unit 32 supplies the signal of the downlinkcontrol channel to a control channel received signal quality estimatingunit 33 and a control data demodulation and decoding unit 37. Further,the inverse spreading unit 32 supplies the signal of the downlink datachannel to a data channel received signal quality estimating unit 35 anda user data demodulation and decoding unit 39.

[0173] After that, the processing proceeds to step S32, and the controldata demodulation and decoding unit 37 demodulates and decodes theindicator ind among the signals of the downlink control channel suppliedfrom the inverse spreading unit 32, and supplies to a transmission modedetermining unit 121, then, the processing proceeds to step S33.

[0174] In this case, if the frequency information is included in thesignal of the downlink control channel, then, the control datademodulation and decoding unit 37 also demodulates and decodes thefrequency information, and supplies to the transmission mode determiningunit 121.

[0175] At step S33, the transmission mode determining unit 121determines whether the indicator ind is “1” or not.

[0176] At step S33, if it is determined that the indicator ind is not“1”, namely, the indicator ind is “0” indicating that there is nopossibility of transmission of the data for the terminal 102, theprocessing proceeds to step S34, then the transmission mode determiningunit 121 presets the transmission frequency P of the mode requestmessage to M frames (preset its cycle to be at every M frames), andsupplies to the data channel received signal quality estimating unit 35.

[0177] After that, the processing proceeds back to step S31, andhere-in-after the similar processing is repeated.

[0178] Accordingly, in this case, the decoding and the demodulation forthe downlink data channel are not carried out.

[0179] On the contrary, at step S33, if it is determined that theindicator ind is “1”, namely, the indicator ind is “0” indicating thatthere is a possibility of transmitting the data for the terminal 102,the processing proceeds to step S35, then the transmission modedetermining unit 121 presets the transmission frequency P of the moderequest message to K frames smaller than M (preset its cycle to be atevery K frames smaller than M frames), and supplies to the data channelreceived signal quality estimating unit 35.

[0180] Accordingly, if the indicator ind is “0”, then the transmissionfrequency P is so as to preset that the transmission cycle of the moderequest message is at every M frames, and if the indicator ind is “1”,then the transmission frequency P is so as to preset that thetransmission cycle of the mode request message is at every K frames.And, in the case of the mode of the present embodiment, as the relationbetween K and M is M>K as described above, if the indicator ind iseither “0” or “1”, the transmission frequency of the mode requestmessage is preset to be either smaller or larger, respectively.

[0181] After that, the processing proceeds to step S36, the control datademodulation and decoding unit 37 starts to demodulate and decode thetransmission mode among the signal of the downlink control channelsupplied from the inverse spreading unit 32, and supplies the resultanttransmission mode to the control unit 38.

[0182] Here, the control data demodulation and decoding unit 37 does notalways demodulate and decode the transmission mode among the signal ofthe downlink control channel, but does start to demodulate and decodethe transmission mode transmitted through the downlink control channelwhen the indicator ind is “1” indicating that there is a possibility oftransmitting the data for the terminal 102. Namely, the control datademodulation and decoding unit 37 carries out the demodulation anddecoding of the transmission mode when the indicator ind is “1”, butdoes not carry out when the indicator ind is “0”. Accordingly, theindicator ind is said to be information representing that there is apossibility of transmitting the data for the terminal 102, and alsocommanding the modulation and decoding of the transmission modetransmitted through the downlink control channel.

[0183] As described above, the demodulation and the decoding of thetransmission mode transmitted through the downlink control channel isnot always carried out, but is carried out when the indicator ind is“1”, so that the load at the terminal 102 is reduced and further, it ispossible to reduce the power consumption.

[0184] After the processing at step S36, the processing proceeds to stepS37, and the control unit 38 determines whether the transmission modesupplied from the control data demodulation and decoding unit 37 is thetransmission mode #0 or not. At step S37, if it is determined that thetransmission mode supplied from the control data demodulation anddecoding unit 37 is the transmission mode #0, then the processingproceeds to step S38, and the control unit 38 controls the user datademodulation and decoding unit 39 so as to QPSK demodulate and furtherto decode with the coding rate R=½ the signal of the downlink datachannel supplied from the inverse spreading unit 32. Further, at stepS38, the user data demodulation and decoding unit 39 supplies the userdata obtained by demodulation and decoding the signal of the downlinkdata channel to an error detecting unit 40, then, the processingproceeds back to step S31.

[0185] Further, at step S37, if it is determined that the transmissionmode supplied from the control data demodulation and decoding unit 37 isnot the transmission mode #0, then the processing proceeds to step S39,and the control unit 38 determines whether the transmission modesupplied from the control data demodulation and decoding unit 37 is thetransmission mode #1 or not. At step S39, if it is determined that thetransmission mode supplied from the control data demodulation anddecoding unit 37 is the transmission mode #1, then the processingproceeds to step S40, and the control unit 38 controls the user datademodulation and decoding unit 39 so as to 16QPSK demodulate and furtherto decode with the coding rate R=½ the signal of the downlink datachannel supplied from the inverse spreading unit 32. Further, at stepS40, the user data demodulation and decoding unit 39 supplies the userdata obtained by demodulation and decoding the signal of the downlinkdata channel to the error detecting unit 40, then, the processingproceeds back to step S31.

[0186] Further, at step S39, if it is determined that the transmissionmode supplied from the control data demodulation and decoding unit 37 isnot the transmission mode #1, then the processing proceeds to step S41,and the control unit 38 determines whether the transmission modesupplied from the control data demodulation and decoding unit 37 is thetransmission mode #2 or not. At step S41, the transmission mode suppliedfrom the control data demodulation and decoding unit 37 is not thetransmission mode #2, then the processing proceeds back to step S31 byskipping step S42.

[0187] Further, at step S41, if it is determined that the transmissionmode supplied from the control data demodulation and decoding unit 37 isthe transmission mode #2, then the processing proceeds to step S42, andthe control unit 38 controls the user data demodulation and decodingunit 39 so as to 16QAM demodulate and further to decode with the codingrate R=¾ the signal of the downlink data channel supplied from theinverse spreading unit 32. Further, at step S42, the user datademodulation and decoding unit 39 supplies the user data obtained bydemodulation and decoding the signal of the downlink data channel to theerror detecting unit 40, then, the processing proceeds back to step S31.

[0188] Next, retransmission request message transmission processing fortransmitting the retransmission request message carried out by theterminal 102 is explained with reference to a flowchart in FIG. 13.

[0189] At first, at step S51, the error detecting unit 40 determineswhether the user data is supplied from the user data demodulation anddecoding unit 39 or not, and if it is determined that it is notsupplied, then the processing proceeds back to step S51.

[0190] Further, at step S51, if it is determined that the user data issupplied from the user data demodulation and decoding unit 39, theprocessing proceeds to step S52, and the error detecting unit 40determines whether the user data supplied from the user datademodulation and decoding unit 39 include any error or not, and suppliesthe detecting result to the retransmission request message generatingunit 41, then, the processing proceeds to step S53.

[0191] At step S53, when the retransmission request message generatingunit 41 receives the detecting result from the error detecting unit 40indicating that there is no error, it generates the retransmissionrequest message having the value of “0”, for example, and supplies tothe retransmission request message inserting unit 42. Further, when theretransmission request message generating unit 41 receives the detectingresult from the error detecting unit 40 indicating that there is someerror, it generates the retransmission request message having the valueof “1”, for example, and supplies to the retransmission request messageinserting unit 42.

[0192] The retransmission request message supplied to the retransmissionrequest message inserting unit 42 is transmitted to the base station 101by the uplink control channel by way of the mode request messageinserting unit 43, the power control bit inserting unit 44, thespreading unit 45, the transmission/reception compatible unit 31, andthe antenna 46, and after that, the processing proceeds back to stepS51, then the similar processing is repeated.

[0193] Next, mode request message transmission processing fortransmitting the mode request message carried out by the terminal 102 isexplained with reference to a flowchart in FIG. 14.

[0194] At first, at step S61, the data channel received signal qualityestimating unit 35 presets “0”, for example, as an initial value to thevariable p which counts the number of frames, then the processingproceeds to step S62. At step S62, the data channel received signalquality estimating unit 35 increments the variable p by “1”, and theprocessing proceeds to step S63.

[0195] At step S63, the data channel received signal quality estimatingunit 35 determines whether the variable p is more than transmissionfrequency P preset at step S34 or S35 in FIG. 12. At step S63, if it isdetermined that the variable p is not more than the transmissionfrequency P, then processing proceeds back to step S62, andhere-in-after similar processing is repeated.

[0196] Further, at step S63, if it is determined that the variable p ismore than the transmission frequency P, namely, the time more than Pframes is to lapse since the previous transmission of the mode requestmessage is carried out, then the processing proceeds to step S64, andthe data channel received signal quality estimating unit 35 estimatesthe SNR, namely the received signal quality, of the signal of thedownlink data channel supplied from the inverse spreading unit 32, andsupplies to the mode selection unit 36, then the processing proceeds tostep S65.

[0197] At step S65, the mode selection unit 36 determines (selects) thetransmission mode based on the received signal quality at the terminalsupplied from the data channel received signal quality estimating unit35, and generates the mode request massage indicating the transmissionmode. This mode request massage is transmitted from the mode selectionunit 36 to the base station 101 by the uplink control channel by way ofthe mode request message inserting unit 43, the power control bitinserting unit 44, the spreading unit 45, the transmission/receptioncompatible unit 31, and the antenna 46, and after that, the processingproceeds back to step S61, then the similar processing is repeated.

[0198] Accordingly, in the mode request message transmission processingin FIG. 14, it is transmitted at every P frames represented by thetransmission frequency P preset at step S34 or S35 in FIG. 12.

[0199] Namely, if the indicator ind is “0”, the transmission frequency Pis set so that the transmission cycle of the mode request message is tobe at every M frames, and if the indicator ind is “1”, the transmissionfrequency P is set so that the transmission cycle of the mode requestmessage is to be at every K frames. Further, in the mode of the presentembodiment, the relation between K and M is M>M, as described above, sothat if the indicator ind is either “0” or “1”, then, the mode requestmessage is to be transmitted with low frequency or high frequency,respectively.

[0200] More specifically, for example, provided that K=1 and K=∞, themode request message is not transmitted when the indicator ind is “0”,and the mode request message is transmitted at every one frame when theindicator ind is “1”.

[0201] As described above, the terminal 102 uses the indicator indindicating the possibility of data transmission, and transmits the moderequest message necessary for determining the adaptive modulation andcoding rate only when there is a possibility of data transmission (forexample, such condition where the data for the terminal 102 is existedat the base station 101, and the data is transmitted to the terminal 102when the radio resources are available), thereby it is possible to saveradio resources. Further, the if it is determined that there is nopossibility of data transmission by the indicator ind (when theindicator ind is “0”), it becomes not necessary to receive informationother than the indicator ind (if the frequency information istransmitted, the frequency information is included) in the control data,thereby, the processing at the terminal 102 is simplified, and it ispossible to realize the low power consumption system.

[0202] Next, power control bit transmission processing for transmittingthe power control bit carried out by the terminal 102 is explained withreference to a flowchart in FIG. 15.

[0203] At first, at step S71, the control channel received signalquality estimating unit 33 estimates the received signal quality whichis the SNR of the signal of downlink control channel, and supplies theestimated received signal quality to the power control bit generatingunit 34, then, the processing proceeds to step S72.

[0204] At step S72, the power control bit generating unit 34 determineswhether the estimated received signal quality of the downlink controlchannel is better than the desirable received signal quality which isthe desirable SNR. At step S72, if it is determined that the estimatedreceived signal quality is not better than the desirable received signalquality, then the processing proceeds to step S73, and the power controlbit generating unit 34 generates the power control bit having a value of“1”. This power control bit is transmitted from the power control bitgenerating unit 34 to the base station 101 by the uplink control channelby way of the power control bit inserting unit 44, the spreading unit45, the transmission/reception compatible unit 31, and the antenna 46,and after that, the processing proceeds back to step S71, thenhere-in-after, the similar processing is repeated.

[0205] At step S72, if it is determined that the estimated receivedsignal quality is better than the desirable received signal quality,then the processing proceeds to step S74, and the power control bitgenerating unit 34 generates the power control bit having a value of“0”. This power control bit is transmitted from the power control bitgenerating unit 34 to the base station 101 by the uplink control channelby way of the power control bit inserting unit 44, the spreading unit45, the transmission/reception compatible unit 31, and the antenna 46,and after that, the processing proceeds back to step S71, thenhere-in-after, the similar processing is repeated.

[0206] Next, with reference to FIG. 16, communication exchange betweenthe base station 101 and the terminal 102 is explained when thetransmission frequencies K and M are set to be K=1, and M=∞,respectively. In this case, K=1 means that the mode request message istransmitted at every one frame when the indicator is “1”, and M=∞ meansthat the mode request message is not utterly transmitted when theindicator is “0”.

[0207] At the base station 101, when there is no possibility oftransmitting the data to the terminal 102, the indicator having a valueof “0” is transmitted. After that, in the base station 101 (FIG. 9), theuser data for the terminal 102 is stored in the data buffer 111, theindicator that is changed the value of “0” to “1” is transmitted to theterminal 102 through the downlink control channel. In this case, in thebase station 101, after the indicator having the value of “1” is startedto transmit, the indicator having the value of “1” is continuouslytransmitted at every frame unit, for example, until the user data forthe terminal 102 is not existed in the data buffer 111 or theretransmission buffer 12. Then, in the base station 101, if the userdata for the terminal 102 is not existed in the data buffer 111 or theretransmission buffer 12, then the value of the indicator is set to be“0”.

[0208] After the indicator is set to be “1”, in the base station 101,the transmission mode (D1) for transmitting the user data for theterminal 102 stored in the data buffer 111, and the transmission mode(D1) is transmitted to the terminal 102. Further, in the base station101, the user data for the terminal 102 stored in the data buffer 111 isencoded and modulated at the adaptive coding and modulation unit 13 inaccordance with the transmission mode (D1) determined by the modedetermining unit 6, and the corresponding amount of the encoded andmodulated user data (D2) is transmitted to the terminal 102 by thedownlink data channel.

[0209] In this case, if the data amount of the user data (D2) isexpressed as X, the data amount (portion depicted with rough slantedlines in FIG. 16) in the data buffer 111 is decreased by the data amountX when the user data (D2) is transmitted. Further, in the base station101, as the encoded and modulated user data (D2) is stored in theretransmission buffer 12 for retransmission as the retransmission data,the data amount of the retransmission buffer 12 (portion depicted withrough slanted lines in FIG. 16) is increased by the data amount X of theuser data (D2).

[0210] At the terminal 102 (FIG. 10), the user data (D2) transmittedfrom the base station 102 is received, demodulated and decoded. Now, ifthere is any error in the user data (D2), NACK (D3) as theretransmission request massage for requesting retransmission istransmitted from the terminal 102 back to the base station 101. In thiscase, the retransmission data (user data (D2)) corresponding to the dataamount X existed in the retransmission buffer 12 of the base station 101is continuously stored in the retransmission buffer 12 until it isconfirmed that the transmission is carried out without any error,namely, until the base station 101 receives ACK (Acknowledge) as aretransmission request message for not requesting retransmission fromthe terminal 102.

[0211] In a mode of the embodiment in FIG. 16, after that, at the basestation 101, the transmission mode (D7) for transmitting next user datafro the terminal 102 stored in the data buffer 111 is determined, andthe transmission mode (D7) is transmitted to the terminal 102. Further,at the base station 101, the next user data for the terminal 102 storedin the data buffer 111 is encoded and modulated in accordance with thetransmission mode (D7) determined by the mode determining unit 6 in theadaptive coding and modulation unit 13, and thus encoded and modulateduser data (D8) is transmitted through the downlink data channel to theterminal 102.

[0212] In this case, if the data amount of the user data (D8) isexpressed as Y, the data amount in the data buffer 111 is decreased bythe data amount Y when the user data (D8) is transmitted. Further, inthe base station 101, as the encoded and modulated user data (D8) isstored in the retransmission buffer 12 for retransmission as theretransmission data, the data amount of the retransmission buffer 12 isincreased by the data amount Y of the user data (D2).

[0213] At the terminal 102 (FIG. 10), the user data (D8) transmittedfrom the base station 101 is received, demodulated, and decoded. Now, ifthere is no error in the user data (D8), and it is normally received atethe terminal 102, then ACK (D9) as the retransmission request massagefor not requesting retransmission (the retransmission message forrepresenting that the transmitted data is normally received andrequesting new user data) is transmitted from the terminal 102 back tothe base station 101.

[0214] The base station 101 erases the retransmission data as the userdata (D8) of the data amount Y stored in the retransmission buffer 12,as the transmission for the user data (D8) is successful when receivesthe ACK (D9).

[0215] In a mode of the embodiment in FIG. 16, after that, at the basestation 101, the transmission mode (D10) for transmitting next user datafro the terminal 102 stored in the data buffer 111 is determined, andthe transmission mode (D10) is transmitted to the terminal 102. Further,at the base station 101, further next user data for the terminal 102stored in the data buffer 111 is encoded and modulated in accordancewith the transmission mode (D10) determined by the mode determining unit6 in the adaptive coding and modulation unit 13, and thus encoded andmodulated user data (D8) is transmitted through the downlink datachannel to the terminal 102.

[0216] In this case, if the data amount of the user data (D11) isexpressed as Z, the data amount in the data buffer 111 is decreased bythe data amount Z of the user data (D11) when the user data (D11) istransmitted.

[0217] Further, in the base station 101, as the encoded and modulateduser data (D11) is stored in the retransmission buffer 12 forretransmission as the retransmission data, the data amount of theretransmission buffer 12 is increased by the data amount Z of the userdata (D11). In addition, in the mode of the embodiment in FIG. 16, thedata amount of the user data for the terminal 102 in the data buffer 111is “0” by the transmission of the user data (D11).

[0218] At the terminal 102 (FIG. 10), the user data (D11) transmittedfrom the base station 101 is received, demodulated, and decoded. Now, ifthere is no error in the user data (D11) like the user data (D8), and isnormally received at the terminal 102, then, ACK (D12) as theretransmission request message representing not requesting theretransmission is transmitted from the terminal 102 back to the basestation 101.

[0219] The base station 101 erases the retransmission data as the userdata (D11) of the data amount Z stored in the retransmission buffer 12,as the transmission for the user data (D11) is successful when receivesthe ACK (D9).

[0220] At the base station 101, when the transmission of the user data(D11) of data amount Z is completed, retransmission operation for theuser data (D2) of the data amount X is started. Namely, the base station101 determines the transmission mode (D4) for transmitting theretransmission data as the user data (D11) stored in the retransmissionbuffer 12 to be the same transmission mode with which the user data (D2)is transmitted at first, and further transmits the transmission mode(D4) to the terminal 102. Further, at the base station 101, the sameretransmission data (D5) as the user data (D2) stored in theretransmission buffer 12 is transmitted through the downlink datachannel to the terminal 102.

[0221] At the terminal 102 (FIG. 10), the retransmission data (D5)transmitted from the base station 101 is received, and demodulated anddecoded. Now, if there is no error in the retransmission data (D5), andis normally received at the terminal 102, then, ACK (D6) as theretransmission request message representing not requesting theretransmission is transmitted from the terminal 102 back to the basestation 101.

[0222] The base station 101 erases the retransmission data (D5) (same asthe user data (D2)) of the data amount X stored in the retransmissionbuffer 12, as the transmission for the user data (D5) is successful whenreceives the ACK (D6).

[0223] As shown in FIG. 16, the base station 101 set the indicator to be“1” when the user data or the retransmission data for the terminal 102is existed in the data buffer 111 or the retransmission buffer 12, andthe terminal 102 that receives the indicator transmits the mode requestmessage back to the base station 101 at every K frames, namely every oneframe in case of the mode of the embodiment in FIG. 16 as thetransmission frequency K is K=1. Further, when the user data orretransmission data for the terminal 102 becomes nothing in the databuffer 112 or the retransmission buffer 12, the base station 101 setsthe indicator included in the control data to be “0”, then, the terminal102 that receives the indicator returns the mode request message atevery M frames, namely in the mode of the embodiment in FIG. 16,prohibits the return of the mode request message as the transmissionfrequency M is M=∞.

[0224] In this case, in the mode of the embodiment in FIG. 16, as thetransmission frequency M is set to be M=∞, so that when the data is notexisted in the data buffer 111 or the retransmission buffer 12, theterminal 102 does not carry out return of the mode request message, butthe transmission frequency M is able to be set to finite value. In thiscase, in the terminal 102, when the indicator designates “0”, the moderequest message is returned to the base station 101 at every M frames.

[0225] As described above, the terminal 102 frequently transmits themode request message determining the transmission mode to the terminal102 based on the indicator transmitted from the base station 101 onlywhen requested from the base station 101. Accordingly, it is possible tosave the radio resources of the terminal 102, and to reduce the powerconsumption.

[0226] Now description will be made on that the processing of theabove-described control data generating unit 112 and the transmissionmode determining unit 121 of the terminal 102 can be effected on thehardware base or software base. If a series of processing is carried outbased on software, a program constituting the software is installed in ageneral-purpose computer or the like.

[0227]FIG. 17 is a diagram showing an arrangement of one embodiment as acomputer having a program for executing the above-described series ofprocessing.

[0228] The program may be recorded in advance in a hard disc 205 or aROM 203 as a recording medium provided within the computer.

[0229] Alternatively, the program may be stored (recorded) temporarilyor permanently in a removable recording medium 211 such as a flexibledisc, a CD-ROM (Compact Disc Read Only Memory), MO (Magneto Optical)disc, a DVD (Digital Versatile Disc), a magnetic disc, or asemiconductor memory. These kinds of removable recording medium 211 maybe offered as a package software.

[0230] The program may be installed from the above-described removablerecording medium 211 into the computer, or alternatively, the programmay be transferred from a download site through an earth satellite suchas a digital broadcast satellite to the computer in a radio transmissionmanner. Furthermore, the program may be transferred from the downloadsite through any network such as a LAN (Local Area Network), theinternet to the computer in a cable communication manner. The computermay receive the program transferred in the above manner at acommunicating unit 208 and the program may be installed in the hard disc205 provided in the computer.

[0231] The computer has a CPU (Central Processing Unit) 202 providedtherein. The CPU 202 is connected with an input/output interface 210through a bus 201. When a user operates an input unit 207 composed of akeyboard, a mouse, a microphone or the like to enter a command and thecommand is supplied to the CPU 202 through the input/output interface210, the program stored in the ROM (Read Only Memory) is executed inaccordance with the command. Alternatively, the CPU 202 loads theprogram on the RAM (Random Access Memory) 204 and executes the program.The program may be obtained by reading the hard disc 205 having theprogram stored therein, by being transferred through the satellite orthe network and received at the communicating unit 208 and installed inthe hard disc 205, or by reading from the removable recording medium 211attached to the drive 209. In this way, the CPU 202 carries out theprocessing in accordance with the above-described flowchart.Alternatively, the arrangement shown in the above block diagram carriesout the processing. Thereafter, the CPU 202 generates the result ofprocessing through the input/output interface 210, for example, to anoutput unit 206 composed of a LCD (Liquid Crystal Display) depending onnecessity. Alternatively, the result of processing may be transmittedfrom the communicating unit 208, recorded in the hard disc 205, orsubjected to any other processing.

[0232] In this specification, the processing steps describing theprogram for making the computer carry out the various processing shouldnot be always processed in the chronological sequence which isillustrated in the flow chart. The description of the presentspecification intends to include a manner of processing in which theseprocessing steps are executed in a parallel fashion or executedseparately (e.g., parallel processing or object oriented processing).

[0233] Further, the program may be processed by a single unit ofcomputer or by a plural units of computers in a distributed manner.Further, the program may be transferred to a computer far away from thecommunication system and executed in the computer.

[0234] Further, the present invention can be applied to various kinds ofcommunication systems in which the base station determines the codingrate and the modulation system for the data to be transmitted to theterminal based on the predetermined information from the terminal.

[0235] For example, in the HDR system, the transmission mode isdetermined in the terminal based on its received signal quality, and themode request message indicating its transmission mode is transmitted tothe base station, therefore, this invention is, of course, applicable toa communication system where the mode request message is transmittedfrom the terminal to the base station, and further applicable to othersuch system as communication system like a W-CDMA system.

[0236] Namely, for example, in the W-CDMA system, the received signalquality message indicating the received signal quality at the terminalis transmitted from the terminal to the base station, and thetransmission mode is determined, at the base station, based on thereceived signal quality indicated by the received signal qualitymessage. The present invention is applicable to a system where thetransmission mode is determined at the base station based on thereceived signal quality at the terminal.

[0237] Further, in the mode of the present embodiment, the transmissionmode and the downlink control channel for transmitting the indicator arenot particularly distinguished, but the transmission mode and thedownlink control channel is able to be transmitted through the samechannel or different channel.

INDUSTRIAL APPLICABILITY

[0238] As described above, according to the present invention, itbecomes possible to save the radio resources.

1. In a transmission apparatus which changes adaptively a modulationrate and a modulation system for data based on a predeterminedinformation transmitted from a receiving apparatus for receiving data,said transmission apparatus is characterized by comprising: determiningmeans for determining a possibility of transmitting data to saidreceiving apparatus; and transmitting means for transmitting to saidreceiving means a possibility information indicating the possibility oftransmitting data to said receiving apparatus, and frequency informationdesignating a transmission frequency of said predetermined information.2. The transmission apparatus according to claim 1, characterized inthat said possibility information and said frequency information arecorresponded to each other; and said transmission means equivalentlytransmits said possibility information and said frequency informationcorresponded to said possibility information by transmitting only saidpossibility information.
 3. The transmission apparatus according toclaim 1, characterized by further comprising: memory means for storingfor storing said data, wherein said determining means determines thepossibility of transmitting the data to the receiving apparatusdepending on whether said data is stored in said memory means or not. 4.The transmission apparatus according to claim 3, characterized in thatsaid data stored in said memory means is used to retransmit the data tosaid receiving apparatus.
 5. In a transmission control method for atransmitting apparatus which adaptively changes a modulation rate and amodulation system for said data based on a predetermined informationtransmitted from a receiving apparatus for receiving data, saidtransmission control method for said transmission apparatus ischaracterized by comprising: a determining step for determining apossibility of transmitting data to said receiving apparatus; andtransmitting step for transmitting to said receiving means a possibilityinformation indicating the possibility of transmitting data to saidreceiving apparatus, and frequency information designating atransmission frequency of said predetermined information.
 6. A computerprogram which has a computer execute a transmission control processingof a transmitting apparatus for transmitting said data to said receivingapparatus based on a predetermined information transmitted from areceiving apparatus for receiving data, said computer program ischaracterized by comprising: a determining step for determining apossibility of transmitting data to said receiving apparatus; andtransmitting step for transmitting to said receiving means a possibilityinformation indicating the possibility of transmitting data to saidreceiving apparatus, and frequency information designating atransmission frequency of said predetermined information.
 7. In areceiving apparatus for receiving data transmitted from a transmittingapparatus which changes a coding rate and a modulation system andtransmits said data, said receiving apparatus is characterized bycomprising: generating means for generating a predetermined informationfor determining said coding rate and modulation system at saidtransmitting apparatus; setting means for setting a transmissionfrequency of said predetermined information based on a possibilityinformation indicating a possibility of transmitting data from saidtransmitting apparatus; and transmitting means for transmitting saidpredetermined information to said transmitting apparatus at thetransmission frequency set at said setting means.
 8. The receivingapparatus according to claim 7, characterized in which: said settingmeans sets a first transmission frequency when there is a possibility oftransmitting the data from said transmitting apparatus, and sets asecond transmission frequency which is lower than said firsttransmission frequency when there is not any possibility of transmittingthe data from said transmitting apparatus.
 9. The receiving apparatusaccording to claim 7, characterized in which: said possibilityinformation is corresponded to frequency information directing atransmission frequency of said predetermined information, and saidsetting means sets the transmission frequency represented by saidfrequency information corresponded to said possibility information. 10.The receiving apparatus according to claim 7, characterized in which:said transmitting apparatus transmits said possibility information, andfurther comprising: receiving means for receiving said possibilityinformation transmitted from said transmitting apparatus.
 11. Thereceiving apparatus according to claim 10, characterized in which: saidtransmission apparatus transmits frequency information designatingtransmission frequency for the predetermined information; said receivingmeans also receives said frequency information; and said setting meanssets the transmission frequency indicated by said frequency informationbased on based on said possibility information.
 12. The receivingapparatus according to claim 7, characterized in which: saidtransmission apparatus transmits a transmission mode indicating thecoding rate and the modulation system for said data; and furthercomprising: demodulation and decoding means for starting demodulationand decoding of said transmission mode corresponding to said possibilityinformation.
 13. In a reception control method for a receiving apparatuswhich receives data transmitted from a transmitting apparatus whichadaptively changes a coding rate and a modulation system and transmitssaid data, said reception control method is characterized by comprising:generating means for generating a predetermined information fordetermining said coding rate and modulation system at said transmittingapparatus; setting means for setting a transmission frequency of saidpredetermined information based on a possibility information indicatinga possibility of transmitting data from said transmitting apparatus; andtransmitting means for transmitting said predetermined information tosaid transmitting apparatus at the transmission frequency set at saidsetting means.
 14. In a reception control method for a receivingapparatus which receives data transmitted from a transmitting apparatuswhich adaptively changes a coding rate and a modulation system andtransmits said data, said reception control method is characterized bycomprising: generating means for generating a predetermined informationfor determining said coding rate and modulation system at saidtransmitting apparatus; setting means for setting a transmissionfrequency of said predetermined information based on a possibilityinformation indicating a possibility of transmitting data from saidtransmitting apparatus; and transmitting means for transmitting saidpredetermined information to said transmitting apparatus at thetransmission frequency set at said setting means.
 15. In a communicationsystem comprising: a receiving apparatus for receiving data; and atransmission apparatus for adaptively changing a coding rate and ademodulation system for said data based on a predetermined informationtransmitted from said receiving apparatus and for transmitting said datato said receiving apparatus; said communication system is characterizedin which: said transmission apparatus includes: determining means fordetermining a possibility of transmitting the data to said receivingapparatus; and a first transmitting means for transmitting to saidreceiving apparatus the possibility information indicating a possibilityof transmitting the data to said receiving apparatus: and said receivingapparatus includes: generating means for generating said predeterminedinformation for determining said coding rate and the modulation systemin the transmitting apparatus; setting means for setting transmissionfrequency of the predetermined information based on said possibilityinformation transmitted from said transmitting apparatus; and a secondtransmitting means for transmitting said predetermined information tosaid transmitting apparatus at transmission frequency set by saidsetting means.